Common rail fuel systems typically employ multiple closed-nozzle fuel injectors to inject high pressure fuel into combustion chambers of an engine. Each of these fuel injectors may include a nozzle assembly having a cylindrical bore with a nozzle supply passageway and a nozzle outlet. A needle check valve may be reciprocatingly disposed within the cylindrical bore and biased toward a closed position where the nozzle outlet is blocked. To inject fuel, the needle check valve may be selectively moved to open the nozzle outlet, thereby allowing high pressure fuel to spray from the nozzle supply passageway into the associated combustion chamber.
One way to move the needle check valve between the open and closed positions includes draining and filling a control chamber associated with a base of the needle check valve. In particular, the control chamber may be filled with pressurized fluid to retain the needle check valve in a closed position and selectively drained of the pressurized fluid to bias the needle check valve toward the open position. When in the open position, the flow of pressurized fuel to the control chamber may be restricted by the base of the needle check valve, thereby minimizing losses associated with pressurized fuel draining to a low pressure reservoir.
One problem associated with this fuel injector arrangement involves efficiency. In particular, although the flow of pressurized fuel to the control chamber may be restricted to minimize losses, some fuel may still be allowed to drain to the low pressure reservoir because the base of the needle check valve does not completely block the flow of pressurized fuel into the control chamber. A method implemented by engine manufacturers to reduce this loss of pressurized fuel and improve efficiency of the affected engine includes changing the shape of the needle check valve base to provide better sealing of the control chamber. One example of changing the needle check valve base is described in U.S. Pat. No. 5,487,508 (the '508 patent) issued to Zuo on Jan. 30, 1996. The '508 patent describes a fuel injector nozzle and tip assembly comprising a check housing defining a cavity with a spray orifice at one end and a control port at the other end. A needle check valve is disposed in the cavity and has a tip at one end for blocking the orifice, and a control port check at the other end for blocking the control port. The control port check is conical in shape for seating against a complementarily shaped seat of the control port.
Although the fuel injector nozzle of the '508 patent may reduce the loss of pressurized fuel and improve efficiency of an associated engine by changing the geometry of the control port check, it may be problematic and expensive. For example, because the seating surfaces of the control port check and control port are conical and designed to engage each other, even slight misalignment between the two surfaces could result in leakage of the pressurized fuel. In addition, the two conical seating surfaces may be difficult and expensive to fabricate.
The fuel injector of the present disclosure solves one or more of the problems set forth above.